The production of fibres from films by splitting has hitherto in practice been confined to the use of polypropylene and high density polyethylene films which possess high splittability in an oriented state. Furthermore, the fibre fineness has been limited by the thickness of the films and because of the complications encountered in the film-making process it has not yet been found practical to use very thin sheets which are generally more desirable.
Furthermore, the fibres produced by the prior art processes have shown a rather low abrasion resistance And resilience, due to the high splittability of the said polymers and to the fact that fissures were introduced which have a tendency to propagate.
Although methods are known for fibrillating films and filaments made from polymers which are more suitable for textile products, e.g. polyamides, and polyethyleneterephthalate and for obtaining fibres which are finer than the thickness of the oriented films from which they have been derived, these methods have not been utilized to any significant extent due to various complications.
The present invention comprises various aspects of a new technique for making split-fibres and the like starting with a sheet structure which is built up from many thin layers of different polymers arranged in interspersed relationship and generally parallel to the face of said sheet structure. This multi-layer structure may be manipulated in different ways before solidification but in any case the solid product still exhibits a distinct multi-layer arrangement which is utilized for forming thin structures by a rubbing action or the like by which the connections between said layers are cleaved. Thus, it becomes possible to form by an economical and simple process split-fibres even from generally unsplittable polymers and to form split-fibres which are much thinner than the film or sheet from which they have been derived.
The invention further comprises a method for forming by co-extrusion a multi-layer sheet or film which is particularly suitable in connection with the subsequent cleaving step but which also can be used independently for the production of laminates.
A still further aspect of the invention comprises the production of bi- or multi-component fibres.